1. Field of the Invention
The present invention relates to a tool for machining by chip removal comprising a body of a hard alloy of cemented carbide, cermet, ceramics, cubic boron nitride based material or high speed steel and a hard and wear resistant metal nitride coating comprising alternating cubic structured (Ti,Al)N layers and cubic structured MeN layers, where Me is one or more of the metal elements Ti, Zr, Hf, V, Nb, Ta, Mo and Al. The coating is grown by physical vapour deposition (PVD) and preferably by cathodic arc evaporation. This invention is particularly useful in metal cutting applications generating high temperatures, e.g., machining of super alloys and stainless steel.
2. Description of the Related Art
Since the early 1980's, TiN-layers have been widely used for surface protective applications. In order to improve the oxidation resistance of these coatings, work began in the mid-1980's with adding aluminium to TiN [see e.g. H. A. Jehn, et al, J. Vac. Sci. Technol. A 4, 2701 (1986) and O. Knotek et. al, J. Vac. Sci. Technol. A 4, 2695 (1986)]. The compound thus formed, cubic-phase (Ti,Al)N, was found to have superior oxidation resistance and enabled greater cutting speeds during machining, prolonged tool life, machining of harder materials, and improved manufacturing economy. Improved coating performance in metal cutting applications has been obtained by precipitation hardening of (Ti,Al)N [see e.g. A. Hörling et al, Surf. Coat. Tech. 191 (2005)] and also disclosed in U.S. Pat. Nos. 7,083,868 and 7,056,602.
Coating optimization has also been obtained by applying different concepts of multilayer as; alternating Ti and Al containing layers (U.S. Pat. No. 6,309,738), oxygen and non-oxygen containing layers (U.S. Pat. No. 6,254,984), one of the layers stacked in the multilayer consists itself of a multilayer (U.S. Pat. No. 6,077,596), alternating nitrogen content (U.S. Pat. No. 5,330,853) or using one metastable compound (U.S. Pat. No. 5,503,912) or as aperiodic multilayer (U.S. Pat. No. 6,103,357).
JP 6136514 discloses a wear resistant multilayered hard coating structure comprising alternating layers of Ti(C, N) and (Al, Ti)(C, N) on the surface of the tool. The coating is deposited by PVD at a relatively low temperature.
The trends towards dry-work processes for environmental protection, i.e., metal cutting operation without using cutting fluids (lubricants) and accelerated machining speed with improved process put even higher demands on the characteristics of the tool materials due to an increased tool cutting-edge temperature. In particular, coating stability at high temperatures, e.g., oxidation- and wear-resistance have become even more crucial.